There is great variety in the devices which are intended to plug into an electrical outlet to heat a volatile substance to release an aromatic vapor as a freshener scent, insect repellant or disinfectant. Some of the variety is related to the problem that electrical outlets may orient the receptacle plugs vertically or horizontally. It is preferable for the device to keep the volatile material above the heating element and from falling out of the insert slots. Thus, several prior art devices are directed to means which make them adaptable for either plug arrangement.
As an early example, U.S. Pat. No. 2,513,919 (Costello) discloses a plug-in vaporizer in which the inlet and exhaust air louvers are arranged at an angle with respect to the plug pins such that the louvers stay in the same vertical relationship whether the plug receptacle are horizontal or vertical. U.S. Pat. No. 2,611,068 (Wellens) discloses a vaporizer where the plug pin assembly can be rotated for the same purpose. U.S. Pat. No. 2,691,716 (also Wellens) discloses a vaporizer in which there are four slots, one at each corner, and cross ribs associated with each slot to define a compartment into which a volatile tablet may be inserted. A resistive heating element lies between the four compartments. Thus, whether the plug recepticals are horizontal or vertical, at least two of the four slots are upright, with their tablet compartments located above the heating element.
Another problem which has produced variations in plug-in vaporizers involves providing the proper temperature and distribution of heat to various compositions and shapes of volatile material. Two prior patents by one of the inventors of the present invention are illustrative of the problem and solutions found in the past. The first aspect of the problem is that a volatile tablet containing an insecticide, for example, may have a different composition and hence a different temperature for its optimum evaporation rate, than a tablet containing a perfume. U.S. Pat. No. 4,467,177 (Zobele) discloses a device which addresses this problem by providing two separate heating platforms, one further from the heating element than the other, to accommodate dissimilar materials which need different temperatures to stay within their desired volatility range. The second problem is the desire to distribute heat relatively evenly over a wide area of the material, which implies some form of heating plate. U.S. Pat. No. 4,251,714 (Zobele) describes the deficiencies in several prior types of heating plate, involving insufficient insulation, need for a grounding prong, and difficulty of assembly; and provides a solution by a T-shaped support housing a longitudinally extending heating element. An aspect of the present invention has similarities to the embodiments of that device.
Recently, gelled liquids containing fragrance oils have become used as room air-fresheners. Such material can be made slowly-volatile at room temperature and can be sealed in a container until ready for use. It can also be made such that the desired volatility is reached at a temperature slightly higher than normal room temperature, a plug-in electric resistance heater. A gelled air freshener of this type is sold under the trade name "GLADE PLUG INS". A container for such gel material which can be used in a plug-in heating unit is disclosed in U.S. Pat. No. 4,849,606.
With gel material air fresheners, the material is usually provided in replaceable, generally rectangular cartridges of approximately 1.5 inch length, 1 inch width, and 0.3 inch depth. A cartridge is inserted into a holder with a hollow chamber generally conforming to the shape of the cartridge. A resistive heating element connected to electrical outlet plug pins supplies heat to warm the material to its desired volatility temperature.
The size and shape of such cartridges and the composition of the gel material again present the problems of adaptability for vertical and horizontal plugs, even heat distribution, and ease of assembly. Consequently, an object of the present invention is to provide an improved heating device for use with a gel air-freshener. Various aspects of this objective and its achievement will be apparent from the detailed description of the best mode. For purpose of facilitating casual review, the following section briefly summarizes the invention in readily understood terms. However, the reader is cautioned that the full extent of invention is only apparent from reading the claims.